Ionization manometer



May 24, 1966 Filed June 8, 1961 10" A A. G. J. VAN OOSTROM 3,253,183

IONIZATION MANOMETER 2 Sheets-Sheet 1 INVENTOR.

A. G.J. VAN OOSTROM y 1966 A. G. .1. VAN OOSTROM 3,253,183

IONIZATION MANOMETER Filed June 8, 1961 2 Sheets-Sheet 2 g 1 I a 1 v 4 6 2 "7- '55??? w m I 55-51:

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INVENTOR ANTONIUS G-J.VAN OOSTROM United States Patent 253, 77 4 Claims. (Cl. 315108) The invention relates to an ionization manometer having a wire-shaped collector electrode which is stretched within an anode shaped in the form of a grid on the outer side of which a filamentary cathode is arranged.

Ionization manometers of the above-mentioned type are known. If the collector electrode is reduced from the conventional value of 150 1. to or less for the lowering of the X-ray limit in such an ionization manometer, this does not completely provide the expected advantage; for, as a result of Xrays from the anode, the thinner collector wire emits fewer electrons, it is true, but at the same time the ion current is reduced when the adjustment and dimensions of the manometer are retained.

It is known that in ionization manometers having a collector electrode arranged on the outer side of the anode, a decrease in the anode voltage for the lowering of the X-ray limit at the same time results in a decrease in sensitivity.

The invention has for its object to provide an ionization manometer which at a very low X-ray limit has a high sensitivity.

In an ionization manometer in which a wire-shaped collector electrode is stretched on the inner side of the grid-shaped anode on the outer side of which a filament cathode is arranged, according to the invention, the voltage difference between anode and cathode amounts to about one fifth of the voltage difference between the anode and the collector electrode, the diameter of the collector-electrode being smaller than 10 The invention is based on the discovery that the thinner the collector electrode, the field between anode and collector electrode in a large area in the vicinity of the anode has a flatter course. This causes the electrons to penetrate more deeply into the space between these two electrodes, it is true but this does not mean that a higher ion current is measured. When the ions are formed they acquire a tangential component in their velocity with respect to the collector electrode. When the ions approach the collector electrode their tangential velocity increases and the field between the anode and collector electrode should be strong enough to surpass the centrifugal force at that velocity. By choosing the ratio between the anode voltage and the collector voltage in accordance to the invention, the course of the field between anode and collector electrode in the vicinity of the collector electrode is such that it is sufficient to force the ions toward the collector electrode. Consequently, also with the thinner collector electrode, the ions current retains a high value and the lowering of the X-ray limit by the thin collector electrode may be fully utilized. Moreover, this limit is lowered by the anode voltage which is lower than usual.

Investigations have proved that it is of advantage to stabilize the voltage between anode and cathode, since at a constant electron current the ion current strongly depends upon the anode-cathode voltage. The voltage 'between cathode and collector electrode or, which amounts to the same, the voltage between anode and collector electrode may, when the condition for the voltage ratio according to the invention is maintained, be

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chosen so that in the area concerned, the collector current is slightly dependent upon the total voltage difference, so that this greater voltage difference need not be stabilized.

According to the invention, the total voltage difference between anode and collector electrode preferably amounts to less than 500 volts in order to restrict leakage cur: rents. The anode-cathode voltage associated therewith then amounts at the most to about volts, which voltage may readily be stabilized. In a manometer in accordance wit-h the invention, the collector electrode is generally connected to earth potential, in order to supply in a simple manner the collector current to a directcurrent amplifier.

The invention will now be described more fully with reference to the accompanying drawing, in which FIG. 1 illustrates the measured results obtained with a manometer in accordance with the invention,

FIGS. 2 and 3 are two sectional views of an ionization manometer tube in accordance with the invention, and

FIG. 4 shows a simple circuit arrangement of such an ionization manometer.

In FIG. 1, the voltage difference between anode and collector electrode is plotted in volts on the abscissa and the collector current is plotted in 10- arnperes on the ordinate. An ionization manometer tube is concerned which has a grid-shaped anode of 18 mm. diameter and of 40 mm. length, the collector electrode having a thickness of 4 The electron current amounts to 50x10- amperes and the gas pressure of the nitrogen in the tube is 2.7 10- mm. The curves I, II, III, IV, V and VI relate to an anode-cathode voltage of 40, 50, 60, 80, and volts, respectively. From these curves it is clearly evident that at a total voltage difference between anode and collector electrode of less than 400 volts, a considerably higher value of the collector current is obtained for the three lower values than at a voltage difference between anode and cathode of 80 volts and more, and consequently the voltage difference between cathode and collector electrode amounts at the most to only two or three times the value of the voltage difference between anode and cathode. Moreover, in the first case, the value of the collector current is in a large area independent of the voltage difference between anode and collector electrode.

Referring now to FIGS. 2 and 3, reference numeral 1 designates the cylindrical bulb having a powder-glass bottom 2; 3 designates the connecting tube to establish the connection with the space in which a pressure has to be measured. Three lead-through pins 4 support a stretched. V-shaped filament cathode 5. Between these pins 4, two pins 6 are arranged which support the grid-shaped anode 7. The ends of the anode are closed with one winding to counteract the escape of ions. Glass-coated leadthrough pins 9 are sealed in two lateral extensions 8, a spring 10 being connected to one of these pins, which spring stretches the tungsten wire 11 as a collector wire inside the anode. A lateral extension 12 lying in the connecting tube 3 comprises a lead-through pin 13 which contacts by means of a spring 14 with a conducting tin oxide layer which extends from the connecting tube 3 to the close proximity of the bottom 2. A wall portion 17 around the lead-through pin 9 is free of this layer.

The glass layer on the pins 9 widens to form tubes 16 which project beyond the welding place between wire and pin and beyond the spring 10.

In a tube as shown in FIGS. 2 and 3 the data of which correspond with those of FIG. 1, at an anode voltage of +55 volts and a collector voltage of 250 volts the X-ray limit amounts to about l0 mm. In a tube having the same collector wire, and an anode having twice as small a diameter, as a result of which the X-ray limit is already raised by a factor 2, at an anode voltage of +150 volt-s and a collector voltage of -26 volts, which are conventional values, the X-ray limit amounts to 1.5 X 10 mm. Consequently, it is found that the choice of the anode and collector voltages considerably afiects the X-ray limit. At the last-mentioned adjustment, the sensitivity is seven time-s smaller than in the tube in accordance with the invention.

FIG. 4 illustrates the manner in which the conducting layer 15 is connected with the cathode. The anode voltage source is designated by 29 and the collector voltage source by 21. The collector electrode is earthed.

What is claimed is:

1. A device for measuring low gas pressures comprising an envelope including means for communicating with a space in which gas pressure is to be measured, a gridlike anode electrode within said envelope, an elongated collector electrode within said. grid-like electrode, said collector electrode having a diameter which is smaller than 10 an electron emitting cathode within said envelope but outside of said grid-like electrode, means applying a given potential between the grid-like electrode and the collector electrode, and means applying a potential between the grid-like electrode and the cathode which is one-fifth that applied between the collector electrode and the grid-like electrode.

2. A device for measuring low gas pressures comprising an envelope including means for communicating with a space in which gas pressure is to be measured, a gridlike anode electrode within said envelope, an elongated collector electrode within said grid-like electrode, said collector electrode having a diameter which is smaller than lQu, an electron emitting cathode within said envelope but outside of said grid-like electrode, means applying a given potential between the grid-like electrode and the collector electrode at which the current flow in the collector electrode is substantially constant as a function of the potential difference therebetween, and means applying a stabilized potential between the grid-like electrode and the cathode which is one-fifth that applied between the collector electrode and the grid-like electrode.

3. A device for measuring low gas pressures comprising an envelope including means for communicating with a space in which gas pressure is to be measured, a gridlike anode electrode within said envelope, an elongated collector electrode within said grid-like electrode, said collector electrode having a diameter which is smaller than 10 an electron emitting cathode within said envelope but outside of said grid-like electrode, means applying a potential of less than 500 volts between the gridlike electrode and the collector electrode, and means applying a potential between the grid-like electrode and the cathode which is one-fifth that applied between the collector electrode and the grid-like electrode.

4. A device for measuring low gas pressures comprising an envelope including means for communicating with a space in which gas pressure is to be measured, a gridlike anode electrode within said envelope, an elongated collector electrode within said grid-like electrode, said collector electrode having a diameter which is smaller than 10 an electron emitting cathode within said envelope but outside of said grid-like electrode, means applying a potential of less than 500 volts between the gridlikc electrode and the collector electrode and at which current flow in the collector electrode is substantially independent of the potential between the collector electrode and the grid-like electrode, and means applying a potential between the grid-1ike electrode and the cathode which is one-fifth that applied between the collector electrode and the grid-like electrode.

References Cited by the Examiner UNITED STATES PATENTS 2,605,431 7/ 1952 Bayard 315-108 2,829,337 4/ 1958 Groendijk. 2,848,635 8/1958 Raible et al. 2,972,690 2/1961 McCoubrey 315-108 GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner.

D. E. SRAGOW, C. R. CAMPBELL,

Assistant Examiners. 

1. A DEVICE FOR MEASURING LOW GAS PRESSURES COMPRISING AN ENVELOPE INCLUDING MEANS FOR COMMUNICATING WITH A SPACE IN WHICH GAS PRESSURE IS TO BE MEASURED, A GRIDLIKE ANODE ELECTRODE WITHIN SAID ENVELOPE, AN ELONGATED COLLECTOR ELECTRODE WITHIN SAID GRID-LIKE ELECTRODE, SAID COLLECTOR ELECTRODE HAVING A DIAMETER WHICH IS SMALLER THAN 10$, AN ELECTRON EMITTING CATHODE WITHIN SAID ENVELOPE BUT OUTSIDE OF SAID GRID-LIKE ELECTRODE, MEANS APPLY- 